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0 °C

Dry phosphinic acid (100 g, 1.52 mol) was dissolved in 100 ml of chloroform and treated with triethylamine (155 g, 1.52mol). The mixture was evaporated and transferred to a three liter flask, containing 750 mL of chloroform. The solution was stirred by means of a mechanical stirrer and the flask cooled to 0° C. The clear solution was treated with triethylamine (277 g, 2.72 mol) followed by trimethylsilyl chloride (281 g, 2.58 mol). Once addition of trimethylsiyl chloride was complete dibenzyl 2-methylenepentanedioate (2) in 150 mL of chloroform was added dropwise over 20 minutes. The low temperature bath was removed and the mixture warmed to room temperature. After 6 hours the thick slurry was filtered and the filtrate cooled to 0° C. The filtrate was then quenched with 5% hydrochloric acid and the organic layer removed. The aqueous layer was extracted with chloroform, the organics combined, dried (MgSO4) and evaporated under reduced pressure to give 55 g of 2,4-di(benzyloxycarbonyl)butylphosphinic acid (6) as a light yellow liquid. The liquid was purified by flash chromatography and eluted using 3:1 hexanes/ethyl acetate containing 5% trifluoroacetic acid to give 40 g (7%) of the desired product. Rf 0.28(3:1 Hex./EtOAc 5% TFA);

1. customThe mixture was evaporated
2. customtransferred to a three liter flask
3. additioncontaining 750 mL of chloroform
4. additionwas added dropwise over 20 minutes
5. customThe low temperature bath was removed
6. temperaturethe mixture warmed to room temperature
7. filtrationAfter 6 hours the thick slurry was filtered
8. temperaturethe filtrate cooled to 0° C
9. customThe filtrate was then quenched with 5% hydrochloric acid
10. customthe organic layer removed
11. extractionThe aqueous layer was extracted with chloroform
12. dry with materialdried (MgSO4)
13. customevaporated under reduced pressure